1. Field of the Invention
The present invention relates to a self-detection charge sharing module, and more particularly, to a self-detection charge sharing module capable of detecting tendency of voltage variation of data lines and performing charge sharing, to raise performance of power saving.
2. Description of the Prior Art
The advantages of a liquid crystal display (LCD) include lighter weight, less electrical consumption, and less radiation contamination as compared to other conventional displays. Thus, LCD devices have been widely applied to various portable information products, such as notebooks, PDAs, etc. In an LCD device, incident lights are polarized or refracted differently when the alignment of liquid crystal molecules is altered. The transmission of the incident light is affected by the liquid crystal molecules, and thus magnitude of the light emitting out of the liquid crystal molecules varies. The LCD device utilizes the characteristics of the liquid crystal molecules to control the corresponding light transmittance and produces gorgeous images according to different intensities and gray scales of red, blue, and green light.
Please refer to FIG. 1, which illustrates a schematic diagram of a conventional thin film transistor (TFT) LCD device 10. The LCD device 10 includes an LCD panel 100, a timing controller 102, a source driver 104, and a gate driver 106. The LCD panel 100 includes two parallel substrates, and the liquid crystal molecules are filled up between these two substrates. A plurality of data lines 110, a plurality of scan lines 112 perpendicular to the data lines 110, and a plurality of TFTs 114 are disposed on one of the substrates. There is a common electrode installed on another substrate for outputting a common voltage Vcom via the common electrode. Please note that only four TFTs 114 are shown in FIG. 1 for simplicity of illustration. In practical implementation, the LCD panel 100 has one TFT 114 installed in each intersection of the data lines 110 and scan lines 112. In other words, the TFTs 114 are arranged in a matrix form on the LCD panel 100. The respective data lines 110 correspond to different columns, and the respective scan lines 112 correspond to different rows. The LCD device 10 uses a specific column and a specific row to locate the associated TFT 114 that corresponds to a pixel. In addition, the two parallel substrates of the LCD panel 100 filled up with liquid crystal molecules can be considered as an equivalent capacitor 116.
The operation of the conventional LCD device 10 is described as follows. First, the timing controller 102 generates data signals for image display as well as control signals and timing signals for driving the control panel 100. The source driver 104 and the gate driver 106 generate input signals for different data lines 110 and scan lines 112 according to the signals sent by the timing controller 102, to control conduction of the corresponding TFTs 114 and voltage differences across the equivalent capacitors 116, so as to change the alignment of liquid crystal molecules and light transmittance. For example, the gate driver 106 outputs a pulse to the scan line 112 for turning on the TFT 114. Therefore, the voltage of the input signal generated by the source driver 104 is inputted into the equivalent capacitor 116 through the data line 110 and the TFT 114. The voltage difference kept by the equivalent capacitor 116 can then adjust a corresponding gray level of the related pixel through affecting the related alignment of liquid crystal molecules positioned between the two parallel substrates. In addition, the source driver 104 generates the input signals, and magnitude of each input signal inputted to the data line 110 corresponds to different gray levels.
If the LCD device 10 continuously uses a positive voltage to drive the liquid crystal molecules, the liquid crystal molecules will not quickly change a corresponding alignment according to the applied voltages. Similarly, if the LCD device 10 continuously uses a negative voltage to drive the liquid crystal molecules, the liquid crystal molecules will not quickly change a corresponding alignment according to the applied voltages. Thus, the incident light will not produce accurate polarization or refraction, and the quality of images displayed on the LCD device 10 deteriorates. In order to protect the liquid crystal molecules from being irregular, the LCD device 10 must alternately use positive and negative voltages to drive the liquid crystal molecules. In addition, the LCD panel 100 has the equivalent capacitors 116, and the related circuit also has some parasitic capacitors owing to its intrinsic structure. When the same image is displayed on the LCD panel 100 for a long time, the parasite capacitors will be charged to generate a residual image effect. The residual image with regard to the parasitic capacitors will further distort the following images displayed on the same LCD panel 100. Therefore, the LCD device 10 must alternately use the positive and the negative voltages to drive the liquid crystal molecules for eliminating the undesired residual image effect, for example column inversion and dot inversion schemes are exploited.
As mentioned above, when the driving voltages of the LCD panel 100 begin to reverse polarities, the LCD device 10 has the largest loading since the source driver 104 consumes the largest amount of current at this time. Generally, charge sharing is exploited to reuse electrical charges and reduce the reaction time that the equivalent capacitors 116 are charged to the expected voltage level, to save power. In the LCD device 10, the source driver 104 evenly allocates electrical charges by controlling transistor switches between two adjacent data lines to achieve charge sharing.
Please refer to FIG. 2, which is a schematic diagram of voltage levels of an odd data channel CH_ODD and an even data channel CH_EVEN next to the odd channel CH_ODD when the LCD 10 is driven by the dot inversion driving approach. As shown in FIG. 2, the X-axis represents time and the Y-axis represents voltage level. The maximum and minimum driving voltage outputted to the equivalent capacitors 116 can be represented by VDD and VGND. The voltage level after charge sharing can be represented by Vavg. If the liquid crystal molecules are driven in the positive polarity, a driving voltage Vp outputted to the equivalent capacitors 116 needs to be between the common voltage Vcom and the maximum driving voltage VDD. On the other hand, if the liquid crystal molecules are driven in the negative polarity, a driving voltage Vn outputted to the equivalent capacitors 116 needs to be between the minimum driving voltage VGND and the common voltage Vcom.
If the LCD panel 100 of the LCD device 10 is driven by the dot inversion driving approach, as shown in FIG. 2, when a driving period ends, the voltage level of the equivalent capacitor of an odd data channel CH_ODD is equal to the maximum driving voltage VDD, and the voltage level of the equivalent capacitor 116 of an even data channel CH_EVEN is equal to the minimum driving voltage VGND, wherein Vcom=0.5 VDD, and VGND=0. Before the next driving period starts, the conventional LCD device 10 first turns on transistor switches coupled between two adjacent data channels to perform charge sharing and neutralize electrical charges stored in liquid crystal capacitors in the end of the previous driving period. Thus, the voltage level of the equivalent capacitor of the odd data channel CH_ODD is pulled from Vp to Vavg. Similarly, the voltage level of the equivalent capacitor of the even data channel CH_EVEN is pulled from Vn to Vavg. Assuming Vp and Vn are equal to the maximum and minimum driving voltage, respectively, Vag=Vcom=0.5 VDD. During the next driving period, the polarity of the odd data channel CH_ODD turns from positive to negative. Since the source driver 102 discharges the odd data channel CH_ODD in advance through charge sharing, only a voltage difference ΔV=−0.5 VDD is provided for driving the liquid crystal molecules to control the gray levels of the relative pixels. Similarly, during the next driving period, the polarity of the even data channel CH_EVEN turns from negative to positive. Since the source driver 102 charges the even data channel CH_EVEN in advance through charge sharing, only a voltage difference ΔV=−0.5 VDD is provided for driving the liquid crystal molecules to control the gray levels of the relative pixels.
However, in the prior art, conventional charge sharing techniques utilize digital signals (i.e. polarity inverted signals) to control data lines with opposite polarities of voltage to perform charge sharing for power saving when polarities of voltages are inverted. These methods of charge sharing can save power only when polarities of voltages are inverted and thus can not apply to applications of only magnitudes of voltages being changed and polarities of voltages being the same, to perform charge sharing for saving power. Thus, there is a need to improve over the prior art.